Conventionally, in medical image systems, such as photon-counting type X-ray computed tomography (CT) apparatus, or positron emission tomography (PET) apparatus, photon-counting type detectors are used, and photon counting is conducted on X-rays, transmitted through the subject, or gamma rays based on an isotope or labeled compound, selectively incorporated in living tissues of the subject.
For example, for photon-counting CT, direct-conversion type semiconductor detectors of cadmium telluride (CdTe), cadmium Zinc telluride (CdZnTe), or the like, or indirect-conversion type detectors of a scintillator, or the like, are used as a detector. Furthermore, for photon-counting CT, for example, an integrated circuit, such as an application specific integrated circuit (ASIC), is provided near the detector so that signals, output from the detector, are processed to acquire data.
For example, the ASIC, used for photon-counting CT, amplifies an output signal from the detector by using an amplifier, shapes its waveform, and then counts the number of incident X-ray photons of each of the windows, which are divided in accordance with the level of the signal. Here, during the photon-counting CT, the counter repeats output (or memory storage) and reset at a constant interval (view) so as to acquire the data on one cycle, thereby acquiring CT images in multiple energy windows.